The number of terrorist attacks worldwide and deaths from such attacks dropped in 2016 for the second straight year, driven by decreases in Afghanistan, Syria, Nigeria, Pakistan and Yemen, the US State Department said on Wednesday.

The total number of terrorist attacks in 2016 dropped 9 per cent compared to 2015, while fatalities caused by the attacks fell 13 per cent, the department said in a report on global terrorism. That was in spite of a series of high-profile attacks in Europe.

The Sunni militant group Islamic State was the deadliest terrorist group last year, carrying out 20 per cent more attacks in Iraq and causing 69 per cent more deaths there compared to 2015.

Data compiled by the University of Maryland for the State Department showed there were a total of 11,072 terrorist attacks worldwide last year, resulting in more than 25,600 deaths. Of those deaths, 6,700 were of perpetrators of the attacks.

Terrorist attacks took place in 104 countries in 2016, but the majority occurred in just five countries: Iraq, Afghanistan, India, Pakistan and the Philippines. Three-quarters of all deaths from terrorist attacks took place in Iraq, Afghanistan, Syria, Nigeria and Pakistan.

The report said a common thread for many of the terror attacks last year “was adherence to violent extremist ideology put forth by a fundamentalist strain of Sunni Islam that perceives itself to be under attack by the West and in conflict with other branches of Islam.”

At the same time, predominantly Shiite Iran was again officially dubbed the leading state sponsor of terrorism. The report cited its longstanding support for the powerful Lebanese Shiite movement Hezbollah, a US-designated terror organisation.

The report cited Hezbollah’s support of Syrian President Bashar al-Assad with troops and supplies as well as its attacks on Israeli soldiers along the Lebanon-Israel border.

In addition, the report said Iran “remained unwilling” to put on trial senior al-Qaeda members whom it has detained.

“Since at least 2009, Iran has allowed al-Qaeda facilitators to operate a core facilitation pipeline through the country, enabling al-Qaeda to move funds and fighters to South Asia and Syria,” it said.

The State Department’s acting coordinator for counterterrorism, Justin Siberell gave no reason for the decline in attacks, but noted the rising pressure last year from coalition forces on the Islamic State group in its Syria and Iraq strongholds.

But as Islamic State loses territory, he said, its fighters and sympathisers are dispersing, and the threat of attacks elsewhere - in new IS locations, and in the IS fighters’ home countries - is on the rise.

“Another feature of the terrorism landscape in 2016 - and this is a continuation of what we saw in 2014 and 2015 - is the exploitation by terrorist groups of ungoverned territory and conflict zones to establish safe havens from which to expand their reach,” said Siberell.

The report spoke positively of recent efforts by Sudan, which was placed on the list of US-designated state sponsors of terrorism in 1993 because of its support of Palestinian and Lebanese militant groups.

“Notwithstanding this history, countering terrorism is today a national security priority for Sudan, and Sudan is a cooperative partner of the United States on counterterrorism,” the report said.

Former US president Barack Obama temporarily lifted sanctions on Sudan in January for six months, suspending a trade embargo, unfreezing assets and removing financial sanctions. President Donald Trump’s administration last week postponed for three months a decision on whether to permanently lift the sanctions.

State Department spokeswoman Heather Nauert told reporters in June that no matter what decision is made on the Sudan sanctions, the designation of Sudan as a state sponsor of terrorism will remain in place.

The only other other US-listed state sponsors of terrorism are Iran and Syria, after Cuba was removed from the list after 33 years.

“It was assessed that there was not sufficient information there to provide a report this year on Cuba,” Siberell said.